1. Cooling system problems
Chapter 3 part 3
Compression testing
Smoke testing
Engine noises
Oil Pressure problems
Cooling system problems

2. Compression testing Can be used when there is
easy access to the spark plug
holes
But may require the help of
a second person
A screw in tester can be more
expensive but does not need a
second person. And is good
when access is difficult.

3. Test procedure
Preferably the engine should be warmed up
The battery must be fully charge
Remove spark plugs ( carefully)
Disable the ignition system and if possible fuel system
Install the compression gauge into the spark plug hole
Hold throttle wide open on carbureted engines
Crank the engine through at least 4 compression strokes
Record each cyl.’s reading

4. Understanding compression readings
If all cyl.’s have good compression and there are no symptoms
Then your done.
Variations of no more than 20% between cyl.’s is considered
Ok in most situations.
If 2 cyl.’s next to each other have low compression, this is
Usually an indication of a blown head gasket.
1 or more low cyl.’s with no pattern is usually burned exhaust
Valves. And will have a rough idle .

5. Wet compression test If a cyl. shows low results your will need to
Perform a wet compression test.
Squirt about 1 tablespoon of oil into the cyl.
That is low the do another compression test
On it.
If the compression now shows normal then
Piston ring problem is indicated.

6. Running compression test
Test the volumetric efficiency
This test is used when a misfire or loss of power
Can’t be identified with a cranking compression test
A typical running test result will be about half the result of a
Cranking compression reading.
Can you tell me why this is?

7. How to perform a running test
Perform a cranking test and record results
Install all spark plug except the one you put the compression
tester in
3) Start the engine and depress and hold the release on the gauge
4) Allow the gauge to stabilize and note the reading
(should be about half of cranking results)

8. Snap compression test
After the running compression test, perform the snap test
Momentarily snap the throttle to w.o.t.
Then allow to return to idle
With the throttle wide open and
The piston still at a relatively low speed
This result should be higher
Snap compression readings should
Be about 80% of cranking results

9. Understanding snap compression test results
Lower snap readings mean the intake system is restricted
Possible causes if on 1 cyl.
Worn cam lobes
Broken valve springs
Problems in all cyl.’s
Can be traced to a restriction in the air intake
System, or a plugged exhaust system

10. Smoke testing Can be used to find Vacuum leaks Oil leaks
Cooling system leaks
Exhaust leaks

11. Vacuum leaks
Engine off
Throttle closed
Disconnect pcv or brake booster hose
Connect smoke machine to this hose
Fill intake with smoke
Look for smoke escaping to locate the leak
Be sure to look under vehicle and inside vehicle

12. Finding exhaust leaks
Use a cone adapter and
Plug any other outlets
It takes about 2 minutes
To fill the exhaust system
Smoke allows you to find
Leaks before they are heard
Manifold leaks can be found
By using a mirror
Cracks are easier found with the engine cold

13. Coolant and oil leaks
Cooling system must be completely drained first
Oil leaks
Plug off pcv and breather hoses first
Or smoke will come out intake through them
Connect smoke machine to oil dip stick tube
watch for smoke leakage

14. Next class
Noises